This invention relates generally to fastening devices, and more particularly concerns screw-accepting anchors for joining workpieces.
Screw and nut devices are commonly used throughout industry to join parts. Standard threaded bolt and nut fasteners usually require two tools to effect the connecting operation; after the screw is inserted through one or more workpieces, an anchor nut member is turned on the screw shank. One tool then engages the nut, and a second tool engages either the screw shank or a screw head, usually located upon an opposite workpiece side, and tightening rotation between the nut and screw is provided by the two tools.
A number of successful attempts have been made to eliminate the need for the nut or anchor-engaging tool. In these fastening systems, the anchors are affixed to a surrounding workpiece in some manner before a screw is inserted into the anchor and screw tightening rotation is begun. In some such devices, the anchor member is glued or otherwise adhesively connected to the surrounding workpiece. Still others rely upon the geometry of the anchor member and the surrounding workpiece aperture to prevent rotation of the anchor in the workpiece as the screw is turned into the anchor. An example of such geometric relationship for preventing rotation is shown in Rapata U.S. Pat. No. 2,788,047 wherein his polygonal shaped shank section 14 engages the complimentary aperture 30. Devices having rotation preventing means in the form of a wrench engaging head is shown in U.S. Pat. No. 2,956,605. The device shown in this latter patent can be used either by restraining rotation through the head and rotating the screw or, alternatively, by restraining the screw and rotating the fastener by means of the head. In each instance, the device requires the secondary restraining means to permit its use in a round aperture.
It is a recognized fact that the cost of producing a polygonal aperture is more expensive in commercial production than to produce a round aperture. Additionally, if repairs or replacements are required in the field, the average serviceman is unable to produce a polygonal or square aperture since the most common tool available to him is a drill capable of producing a round hole. Thus, the need for a screw retaining means which is acceptable in a round hole and which will not spin when the screw is introduced into the bore thereof is well recognized. Further, to be commercially successful, fastening devices must minimize the number of parts and work operations required in a screw and anchor assembly operation. Thus, the need for adhesives, extra tools or parts is often considered a drawback. Moreover, inadvertent spinning of the anchor in the workpiece caused by improper application of assembly forces to the screw and anchor slows assembly operations or repairs and contributes to manufacturing and maintenance costs, since the operation must be started over again.
One such attempt at the solution of this problem was my previously issued U.S. Pat. No. 3,893,365 in which I provided a one-piece plastic screw anchor having the screw receiving bore formed parallel but offset from the axis of the shank. While this is an acceptable solution and provides a modicum of adjustability due to the off center relationship of the two axes, it does have drawbacks where it is desired to have a predetermined location for the screw axis and required a bit of adjustment for orientation to accept the screw through the secondary workpiece being supported and fastened.